"It is a huge and responsible task Stoltenberg has received today," Solberg said in a statement.

A two-time Norwegian prime minister, Stoltenberg became a recognizable face on the international scene with his dignified response to the twin terror attacks that killed 77 people in July 2011.

Stoltenberg's pledge at the memorial service to combat the atrocity with "more democracy, more openness, and more humanity" helped salve the country's wounds.

His coalition suffered a year later when an independent inquest into the bomb and gun attacks by right-wing fanatic Anders Breivik found a litany of failures by police and security services that might have disrupted or even prevented the slaughter. By September 2013, Stoltenberg's coalition government had been ousted by a combination of conservatives and populists as the Norway tilted right.